It is often desirable or necessary to mount a shaft extending into a closed system such that rotary motion can be imparted to the shaft from a location outside the system as the mount for the shaft remains sealed to the system. This is especially true in vacuum systems where it would be clearly impractical to shut the system down to enter the system merely to rotate the shaft. For instance, with a test specimen mounted on the shaft in the system, it may become necessary or desirable to change the operative position of the sample on the shaft with respect to a predetermined reference. For this purpose, rotary motion feed-through mechanisms have been known and used in the past.
A typical mechanism for this use has been one in which the feed-through or rotary shaft of the mechanism has one short end segment which is bent out of longitudinal alignment with the main, straight segment so that the bent segment can be coupled by bearing means in a groove in the beveled face of a rotary element to which a knob or stepper motor can be attached. Thus, by rotating the knob or actuating the stepper motor, the rotary element is rotated to, in turn, rotate the bent segment of the shaft and thereby the shaft itself. While this arrangement has been found to be satisfactory in some cases, it has drawbacks. Among these include the fact that it is difficult to bend the shaft accurately to a predetermined angle, such as 10.degree.. When the shaft is bent, it is subject to internal structural stresses which weaken the shaft. Thus, when torque is applied to the shaft, such torque tends to straighten the shaft and the rotational effect imparted to a part coupled with the shaft is diminished, at least to a certain extent. Moreover, the rotary element to which the bent shaft segment is coupled must be machined accurately to form the beveled face thereof so that the face is properly positioned relative to the bent shaft segment. This requires precision machining and a considerable amount of time and expense.
Because of the foregoing drawbacks, a need exists for improvements in such mechanisms and the present invention satisfies such a need.